Belt tensioner



Dec. 2; i953 Fild June 2o, 195o R. P. HORAN BELT TENSIONER 2 Sheets-Sheet l INVENTOR. RALPH P. HORAN jvc-vd 9%7...

ATTORNEYS Dec. 22, 1953 R. P. HoRAN 2,663,195

BELT TENSIONER Filed June 20, 1950 2 Sheets-Sheet 2 INVENTOR. RALPH P, HoRAN ATTOR N EYS tionS. A

Patented Dec. 22, 1953 -nuN1TED-srATEs PATENT OFFICE.g

v"BELT TENsIoNER Ralph?. Horan, Detroit, Mich., assignor to Eaton .Manufacturing Company, Cleveland, Ohio, a

` corporation of- Ohio applicati-@June zo, 195o, serial No. k169,203 1o claims. (c1. 'i4-242.11)

This invention relates to the tensioning of pulley driven belts and more particularly tol mechanism 'for essentially maintaining av constant belt tension for a given range of tension pulley posi- VBroadly the' invention comprehends the provision of a belt tensioning mechanism comprising a linkage arrangement wherein the geometric relationship of the links is such, together with the constant loading of fone of the links effective tomaintain a constant beltftension and a constant maxim-um driving torque capacity when the belt length changes.

Although numerous belt tensioning devices have been devised, none have achieved the desirable results attained'by'the presently devised .mechanism through vthe provision y of a specic geometric relationship of a two arm linkage mechanism wherein the link arms are arranged to remain substantially parallel to the slack side rof the belt with one arm having a'xed length and pivot axis and the 'other arm being loaded .by an external source to exert a constant force parallel to the arm over a range of beltzdeflections. f

Among the several objects of the invention is .the provision of a belt tensioninggmechanism that occupies a minimum of space; that is, provided with ample friction in its bearings to over- .come any tendency toward the vibration thereof due to belt nap at high speeds; and, that is capable of maintaining a constant belt tension and a constant maximum driving torque capacity.

lOther objects and advantages ofthe invention will appear from thefollowing description taken in connection with the drawings, forming a part of the specification; and in which,

Fig. 1 isa sidefelevation View of a belt tensioning mechanism, constituting `the invention, partly in section as applied to a pulley drivenV belt arrangement Fig. 2 is an enlarged vertical cross-sectional view taken substantially along'lines 2.-'2fof Fig.

Fig.` 3 is an enlarged'vertical cross-sectional view taken substaam`i'.iallyV along lines 3-.3 of Fig. 1. This belt tensioning mechanism was devised for the purpose of providing a simple linkage arrangement which was effective to achieve the desirable condition of constant belt tension or constant maximum driving torque capacityof a pulley driven belt. The linkage arrangement comprises two link arms, one of which is xed as to length and pivot axis Whereas the other link arm which is freely pivoted at the free end of thefirst link arm having a tensioning pulley upon the joint pivot thereof is` extensible in length and movable -upon a xed pivot axis. The extensible link arm is loaded so as to exert a constant force parallel to the arm over a range of belt deections. The link arms are so-positioned to one another and the pulley driven belt to which applied and made of predetermined arm length such that they are maintained substantially parallel to the slack Yside of the belt thereby f providing a geometric arrangement which together with the loading of the extensible link arm provides for the substantially constant maximum driving torque capacity of the mechanism.

By providing a desirable friction in the bearings for the mechanism it is possible to overcome any tendency toward vibration of the mechanism due to belt nap at high speeds.

Referring to the drawings for more specific details ofthe invention I0 represents a belt tensioning mechanism as applied to a pulley driven belt arrangement I2. I

'I'he pulley driven belt arrangement comprises a driving pulley I4, a driven pulley I6 of smaller diameter than pulley I4 and an -endless belt I8 driven about the pulleys for the transmission of rotation therebetween. v

The belt tensioning mechanism IIJ which is applied to the belt I8 so as to maintain a con- `stant tension thereon comprises two link varms porting upon the pivot shaft 25-thereof a tensioning pulley 26 adapted to have bearing engagement upon the external surfaces of the belt on the clock side thereof as viewed in Fig. 1.

The link arm 20 is pivoted at'end 28 thereof upon a bearing yoke 30 which is, in turn, suitably xedly securedupon a stationary plate 32. Link arm 22 is in two parts, part' 34 pivoted on shaft 25 and-an extended rod 36 integrally connected with part 34. 'I'he rod 36 is received in a bore 38 ofa spring retainer 40 and a bore 42 of abolt 44 for free axial movement thereto lwith a compression coil spring 46 arranged intermediate a hub portion 48 of link arm part 34 and spring retainer 40 in telescoping relation about rod 3S. The bolt 44 is, in turn, threadingly secured in an adjustable pivot shaft 50 with one end abutting the axial extremity of spring retainer 40 opposite from the spring bearing point thereon. The pivot shaft 50 is mounted in a bearing yoke 52 which like bearing yoke 30 is suitably secured upon plate 32.

It will be observed in viewing Fig. l that the bearing yokes 30 and 52 are so arranged as to lie substantially in aline intercepting the belt tangent and center of each pulley, with the belt in straight line connection between the pulleys on the slack side thereof. Slight variation from the true positioning thereof is necessary to eliminate any possibility of interference of the llinkv arms with the belt as the flink' arms arepivoted and the tensioning pulley moved to maintain constant tension on the belt as well as to account for a shifting of the line intercepting the pulley center and tangent point of the belt as the belt slackens. By so arranging the `pivot axes for the link arms in close proximity to the belt and proportioning the link arms, the arms are made to lie substantially parallel to the slack side of the belt for a range of belt deflections.

The spring 4E in its position between the link arm 22 and :spring retainer positioned by the bolt 44 is freeto exert'a constant load on the arm lalong the axis thereof, the component force of which is applied by tensioning pulley 25 to the belt such that because ofthe reaction of they belt being equal and opposite to the force of the pulley 26 applied to the b elt and the parallel arrangement of the link arms, the tension in the slack side ofA the belt will be an equal and opiposite force to the constant load. applied by spring 46. v

Under conditions wherein itisconceivable that the stretchv of the belt might change its length when the driving pulley is varied 'between high and low ranges of speed, the tensioning mechanism is operable to maintain a substantially constant driving torque capacity even though the .length of the arm 22 from its pivot point varies slightly.

The rod 35,'as shown by Fig. l, is initially set for one belt length or tensioning position wherein it extends a Apredetermined distance beyond the nut end 54 of the bolt so that if or-as `the -belt lengthens beyond this predetermined movement of the rod relative to the bolt when ythe rod disappears into the bolt-'at the nut end thereof,

-azreadjustment of `the rod and bolt'for the proper compression height of the spring can `be made so vthat a desired constant force of the spring can be exerted and a substantially constant tension of `the belt can be maintained;

The belt tensioning mechanism is effectiveto provide 4for a substantially constant tensioning of the belt or constant maximum driving torque capacity over a considerable range ofv belt length change even taking into account that as thebelt flengthens, the wrap around on the small pulley increases such that even if a slightly greater load might be required when the belt has lengthened anappreciable amount if all other conditions Vremained the same, the wrap around on the small pulley` compensates for the load difference thereby not requiring the load difference to maintain the `constant tension desired.

v-liy so arranging the link armsin close parallel proximity to the slack side .of the belt'the space occupied thereby is a minimum and so adapts the belt tensioning mechanism advantageously to engine driven accessories such as superchargers, compressors and the like where space is usually limited.

Y The link arms in their bearing relation to one another and the bearing yokes with which they are respectively associated have sufficient frictional resistance imposed thereon to their free movement eifective to overcome any tendency toward the vibration thereof due to belt flap at high speeds.

Although thebelt tensioning mechanism as lhere disclosed isdirected .specifically tothe provision of a coil spring for applying the constant load for the proper controlled operation thereof,

it is conceivable that any of several loading mediums such as hydraulic fluid or the like under l pressure could vequally as well be utilized, and

further :even though the mechanism is shown in Lone illustrated application, it is susceptible .of numerous changes in structural embodiment and application as will readily appear to those skilled in lthe art. The invention is, therefore, limited only as indicated by the scope of the appended claims.

WhatI claim is:

l. In a belt tensioning mechanism,'an arm having a fixed lpivot axis, a second arm freely pivoted at the free end of the 'rst arm, 'an idler pulley pivoted at the pivot connection of 'the arms, and constant load vmaintainable means exerted on thesecond arm Yparallel thereto said arms being arrangedand maintained substantially parallel to the slack side ofthe belt which the mechanism isadapted to tension with 'the pulley in engagement'with the belt'at its external periphery on the slack side thereof.

2. .A belt tensioning mechanism 'according to claim l wherein the second arm 'is pivoted .on and axially movable relatively'to a fixed bearing :pivot therefor. v y

3. A mechanism according to claimlwherein the. constant load maintainable means is an adjustable height coilspring.

4. A mechanism according to .claim 2 wherein the vpivot axis of therst arm and bearing pivot for the second arm lie substantially respectively in lines passing through the axis of the driving and driven pulleys of a vbelt drive 'arrangement and the normal tangent of the belt to the lpulleys and wherein the arms .are arranged parallel .to the slack side of the belt which the idler` pulley engages externally of the belt. g

5, A mechanism according to claim l wherein the second arm is axially slidable in a fixed pivot postand is axially-resilientlybased away .from thepost by a coil spring, inserted between `the .post and arm, exerting a constant load thereon.

6. A mechanism according to claim 5 wherein adjustment means are providedfor setting the spring to a desired .compression height.

7. A mechanism according to claim 6 wherein means are provided fon observing the axial movementv of' "the -second arm relative to the spring adjustment means.

`8. A mechanism according to claim l wherein the second arm is axially movable in an .adjustment bolt threaded in a xed pivot post and a constant load coil spring is arranged intermediate a portion of Ythe bolt and second ar-mbiasin the bolt and second arm axially apart.

9. VA mechanism laccording, to claim 8 wherein the free end `of the `second .arm Aextends axially .beyond the bolt apredetermined#distance are gif

10. In a belt tensioning mechanism, an arm having a fixed pivot axis, a second arm freely pivotal at the free end of the first arm, a pivotal fixed axis bearing support for the second arm, an idler pulley pivotal at the pivotI connection of the arms, and constant load maintainable means exerted on the second arm, said arms being arranged and maintainable substantially parallel to the slack side of a belt Which the mechanism is adapted to tension with the pulley in engagement with the belt at its external periphery on the slack side thereof and wherein the arms are in line With one another and they lie 6 parallel to a portion of the belt to be tensioned when there is no slack therein.

RALPH P. HORAN.

References Cited in the le of this patent UNITED STATES PATENTS 

